Apparatus, and an associated method, for preserving communication service quality levels during hand-off of communications in a radio communication system

ABSTRACT

A mobile station is configured to transmit a sequence of data packets over a wireless network. The station includes a data sequence expander. The expander receives an indication of a pending hand-off for the mobile station from a first network access point to a second network access point and estimates an amount of time prior to occurrence of the hand-off. The expander inserts a number of delay packets into the sequence of data packets in response to receiving the indication of the pending hand-off. The number of delay packets is determined based on the estimated amount of time prior to the occurrence of the hand-off such that the insertion of the delay packets into the sequence of data packets will cause a delay that corresponds to the amount of time prior to occurrence of the hand-off.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. application Ser. No. 13/085,532, filedApr. 13, 2011, which is a continuation of U.S. application Ser. No.12/827,493, filed Jun. 30, 2010, now U.S. Pat. No. 7,948,950, which is acontinuation of U.S. application Ser. No. 10/915,994, filed Aug. 11,2004, now U.S. Pat. No. 7,773,561, which claims priority ofPCT/GB2003/003576, filed Aug. 15, 2003, all the above applicationshereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to a manner by which to preserveservice quality levels of communications of real time data streams in aradio communication system during handoff of communications betweenserving and target entities. More particularly, the present inventionrelates to apparatus, and an associated method, by which to add to, i.e.stuff, a sequence of communication data symbols forming a real time datastream with extra data symbols. The sequence is communicated as a realtime stream during the handoff of communication.

Brief service interruption during handoff that would otherwise benoticeable in playing out of the real time stream is less likely to benoticed. By stuffing the sequence with the extra data symbols, thesequence, when acted upon by a receiving node, plays out as a real timestream. When the extra data symbols correspond in length at least withthe length of the service interruption, appearance of the serviceinterruption is not noticed at a receiving node.

BACKGROUND

The need to communicate is an endemic need of modern society. Data mustbe communicated, sometimes between very widely spaced apart locations,to effectuate many varied communication services. Communication systemsare used to effectuate the communication of the data. A communicationsystem is formed, at minimum, of a sending station and receiving stationinterconnected by way of a communication channel. Many different typesof communication systems have been developed and deployed through whichto effectuate many different types of communication services.

As technological advancement warrants, new types of communicationsystems have been developed and deployed. Technological advancementscontinue and communication systems that embody such advancementscontinue to be deployed.

Many modern communication systems utilize digital communicationtechniques. Digital communication techniques provide several inherentadvantages over analog communication techniques. Perhaps mostsignificantly, increased communication efficiency is possible throughthe use of digital communication techniques. And, as result, thecommunication capacity of a communication system that utilizes digitalcommunication technique is generally significantly greater than thecommunication capacity available to a corresponding communication systemthat utilizes analog communication techniques.

A radio communication system is a type of communication system in whichthe communication channels interconnecting the communication stationsthereof form radio channels, defined upon a radio air interfaceextending there between. The infrastructure required to implement aradio communication system is generally less than that required of acorresponding wireline counter part. And, the cost required to deploythe infrastructure of the radio communication system is generally lessthan the corresponding cost to deploy the wireline counterpart.Additionally, a radio communication system is amenable forimplementation as a mobile communication system in which mobility ofcommunication is provided.

A cellular communication system is a type of radio communication system.The network infrastructures of cellular communication systems have beendeployed over significant portions of the populated areas of the world.Successive generations of cellular communication systems have beendeveloped and deployed. And, successor generation systems are undergoingdeployment or standardization.

Other wireless networks have also been deployed, sometimes incorporatingvarious aspects of cellular communication systems. For instance,wireless local area networks (WLANs) as well as wider-area, wide areanetworks (WANs) are increasingly being used to communicate data, bothvoice data and non-voice data. An IEEE (Institute of Electrical andElectronic Engineers) 802.11 standard, and variants thereof, definesoperating parameters by which many wireless LANs are operable. WLANs areimplemented at both licensed and non-licensed bands of theelectromagnetic spectrum. When a user has a choice of communicating byway of a commercial, cellular communication system and a private WLAN,use of a private WLAN is sometimes preferred for the reason thatcommunication costs associated with the private network are generallyless than corresponding costs to communicate by way of a commercialcellular communication system.

Some wireless local area networks provide for communication hand offs topermit continuation of communications with a mobile node as the mobilenode travels throughout an area encompassed by a plurality of fixed siteradio transceivers, sometimes referred to as access points (APs).Sometimes brief service interruptions occur when the communications arehanded off from a serving access point to a target access point. That isto say, the serving access point is disassociated with thecommunications, and the target access point becomes associated with thecommunications. When the communication of the data is not timesensitive, the brief service interruption is usually insignificant.However, when the communication of the data is time sensitive, such aswhen the communication service forms a telephonic voice communication,the interruption is noticeable and potentially reduces the quality ofservice (QoS) of the communication session.

As an example, the service interruption, i.e., the period of time duringwhich a channel is unavailable to communicate the data, might be as longas 300 ms. If the packets of the data communication are of lengths suchthat the packets are communicated once every 20 ms, then, for a 300 msinterruption, approximately 15 real time packets are delayed or droppedduring the handoff of communication. As the communication range of anaccess point might be 30 meters, or less, multiple handoffs betweensuccessive access points might be required during a single communicationsession. Repeated service interruptions, and their noticeable effectsmight well have a compounding effect on a user perception of the qualityof the communications as well as a quantitative QoS level.

A manner by which to preserve the quality of service level ofcommunications during hand-off of the communications between source andtarget access points, or other entities, would therefore be beneficial.

It is in light of this background information related to communicationhandoff procedures that the significant improvements of the presentinvention have evolved.

SUMMARY OF THE INVENTION

The present invention, accordingly, advantageously provides apparatus,and an associated method, by which to preserve service quality levels ofcommunications in a radio communication system during handoff ofcommunication between serving and target entities.

Through operation of an embodiment of the present invention, a manner isprovided by which to stuff extra data symbols into a sequence ofcommunication data symbols that is to be communicated as a real timedata stream during handoff of communication between the source andtarget entities.

Connection delays resulting in service interruptions that wouldotherwise be noticeable in playing out of the real time stream are lesslikely to be noticed by a user of a receiving node. The extra datasymbols form part of the sequence that is played out at the receivingnode as the communications are handed off from the serving entity to thetarget entity. That is to say, by stuffing the sequence with the extradata symbols, the sequence, when acted upon by a receiving node, playsout as a real time stream. When the extra data symbols are added innumbers to be of a length at least as great as the length of the serviceinterruption, the service interruption is not noticed at the real timenode. Quality of service levels are not adversely affected as they wouldotherwise be if no compensation were made for the service interruption.

In one aspect of the present invention, data stuffing operations arecommenced prior to handoff of communication from the serving entity tothe target entity. Detection is made of the pendency of the handoff ofcommunication. For instance, pendency of the handoff of communicationsis detected as a result of mobile node signal strength, or otherappropriate signal indicia measurements made during otherwise normaloperation of a mobile node. Or, indications of the pendency of thehandoff of communications are, alternately, provided by the networkinfrastructure of the communication system. Preemptive detection of thehandoff thereby initiates the data stuffing operations.

In another aspect of the present invention, a de jitter buffer is usedat which to buffer data symbols of a communication sequence that iscommunicated pursuant to effectuation of a communication service. Thedata sequence buffered thereat is stuffed with additional data symbols,collectively to increase the length of the sequence. Through appropriateselection of the number of additional data symbols to be stuffed intothe sequence, brief service interruption is compensated for by theadditional data symbols added to the sequence. When, for instance, theadditional data symbols added to the sequence are of lengths thattogether are at least as great as the service interruption duringhandoff, the noticeable effects of a connection interruption are notnoticed by a user of the receiving node.

The de jitter buffer is embodied, for instance, at a proxy devicecoupled to the network part of the communication system. When a proxydevice is utilized, the proxy device functions as an intermediarybetween a mobile node and a correspondent node. The correspondent nodeis, for instance, an “unaware” node. That is to say, the correspondentnode need not be aware of the handoff of communications. A data sequenceoriginated at the mobile node is communicated by way of the radio airinterface and delivered to the proxy device. At the proxy device, thedata sequence is buffered, and the additional data symbols are addedthereto. Alternately, the additional data symbols are added to thesequence at the mobile node. And, when data is originated atcorrespondent node for communication to the mobile node, the data isdelivered to the proxy device whereat the additional data symbols areadded to the data sequence, prior to forwarding of the data sequence onto the mobile node. The additional data symbols alternately are added tothe data sequence once delivered to the mobile node.

In an implementation in which the de jitter buffer is embodied at themobile node, the data stuffing operations are performed entirely at themobile node. Upon detection of the pendency of a handoff ofcommunication, data sequences that are expected to be communicatedduring the handoff are stuffed with the additional data symbols.

A functional entity, a data sequence expander, is utilized to add thedata symbols to the data sequence. During operation, selection is madeas to the number of data symbols that are to be added to the datasequence. In an exemplary implementation, the number of data symbolsadded to the sequence corresponds to the length of time of the expectedservice interruption. And, the expander also selects the manner by whichthe data sequence is expanded. In one implementation, the data symbolsthat are added to the data sequence are copies of data symbols containedin the data sequence. And, in the exemplary implementation, the datasymbols that are selected to be copied and stuffed into the datasequence correspond to silent data symbols. That is to say, the datasymbols that are selected to be stuffed into the data sequence are ofsymbol values corresponding to periods of silence in the data sequence.And, the data sequence expander further selects at where in the datasequence that the data symbols are added. In the implementation in whichthe additional data symbols correspond to silent periods, the additionaldata symbols are stuffed into portion of the data sequence that are ofsymbol values corresponding to silent periods. Thereby, the delay addedto the data sequence is least likely to be detected by a user of areceiving node.

In another aspect of the present invention, unstuffing operations areperformed to return the data communication operations to normalsubsequent to the handoff of the communications. That is to say, thedelays introduced into the communications by the stuffing of theadditional data symbols into the data sequence are removed by unstuffingoperation. The unstuffing procedure acts to compress the real time datastream, i.e., the sequence of data is compressed to return the delayback to normal. In one implementation, a data sequence compressor isutilized to identify packets that are unstuffed, or otherwise not playedout in real time, upon completion of the handoff procedure and thecommunication of the data continues normally. The data unstuffing isperformed at a proxy device in an implementation that utilizes a proxydevice formed in part of the network infrastructure of the communicationsystem. And, in an other implementation, the unstuffing is performed atthe mobile node.

Thereby, a manner is provided by which to preserve the service qualitylevel of communications between communicating nodes of a radiocommunication system during handoff of communication from a servingentity to a target entity. The procedures are performable with anunaware node, that is, a node that is unaware of the handoff ofcommunications. Thereby, only a mobile node, forming one of the nodes ofthe communicating nodes, is aware of the handoff of communications.

In these and other aspects, therefore, apparatus, and an associatedmethod, is provided for a communication system. The communication systemhas a mobile node that communicates a first sequence of communicationdata symbols pursuant to effectuation of a communication service with anetwork part. The network part has a serving access point with which themobile node initially communicates and at least a first target accesspoint with which communications continue subsequent to handoff ofcommunications thereto. Improved perceived service quality levels ofcommunications are facilitated during handoff of the communications fromthe serving access point to the target access point. A data sequenceexpander is adapted to receive indications of pendency of the handoff ofthe communications and to receive representations of the first sequenceof the communication data symbols communicated pursuant to theeffectuation of the communication service. The data sequence expander isselectably for adding expanded data symbols to the first sequence of thecommunication data symbols responsive to detection of the indication ofthe pendency of the handoff of the communication, thereby to form afirst expanded sequence. A more complete appreciation of the presentinvention and the scope thereof can be obtained from the accompanyingdrawings that are briefly summarized below, the following descriptionsof the presently-preferred embodiments of the invention, and theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a functional block diagram of a radio communicationsystem in which an embodiment of the present invention is operable.

FIGS. 2-1, 2-2, 2-3, 2-4, and 2-5 illustrate representations of stuffingoperations performed during operation of an embodiment of the presentinvention.

FIGS. 3-1, 3-2, 3-3, 3-4, and 3-5 illustrate representations, similar tothose shown in FIG. 2, but here of unstuffing operation, also performedduring operation of the embodiment of the present invention.

DETAILED DESCRIPTION

Referring first to FIG. 1, a communication system, showing a generallyat 10, provides for radio communication with mobile station, of whichthe mobile station 12 is representative. And in the exemplaryimplementation, the radio communication system forms a WLAN (WirelessLocal Area Network) that operates, generally, pursuant to a version ofthe IEEE (Institute of Electrical and the Electronic Engineer) 802.11operating specification. The communication system is also representativeof other types of communication systems, i.e. communication systems thatare operable pursuant to other operating specifications. Accordingly,while operation of an embodiment of the present invention shall bedescribed with respect to its implementation pursuant to the operatingspecification of the IEEE 802.11, or variant, standard, the teachings ofthe present invention are analogously applicable in other types ofcommunication systems.

Data is communicated during operation of the communication systembetween a mobile station and network part of the communication system.And, more particularly, pursuant to a communication session, a mobilestation communicates with a fixed-site radio transceiver, referred to asan access point (AP) 14, that forms part of the network portion of thecommunication system. The network portion includes a plurality of accesspoints, of which two are shown in the Figure. The data is communicatedby way of radio channel defined upon radio links, shown at 16, thatextends between the mobile station and an access point. Datacommunicated by the mobile station to an access point of the networkportion is sometimes referred to as being communicated on a reverse linkchannel. And, data communicated by an access point of the networkportion to the mobile station is sometimes referred to as beingcommunicated upon a forward link channel.

Each of the access points 14 of the network portion of the communicationsystem defines a coverage area, sometimes referred to as a cell. When amobile station is positioned within a cell associated with an accesspoint, communications of the mobile station with the network portion ofthe communication system are generally effectuated with the access pointthat defines the cell within which the mobile station is positioned.

The network portion of the communication system also includes a controlhub 18 to which the access points 14 are connected. The control huboperates, amongst other things, to control operation of the access pointand, thereby, communications in the WLAN. The control hub is embodied,for instance, at a computer server. And, the control hub, in turn, iscoupled to a packet data network (PDN) 24. The packet data network is,for instance, comprised of the Internet backbone. A correspondent entity(CE) 26 is representative of a communication device with which a mobilestation 12 communicates during a communication session to effectuate acommunication service. The correspondent entity is, course, positionableelsewhere, such as within the WLAN, or at another location of thecommunication network.

Due to the inherent mobility of a mobile station, the mobile stationmight travel out of the cell defined by one access point and into a celldefined by another access point. A communication handoff from a servingaccess point to a target access point is effectuated to permit continuedcommunication with the mobile station as the mobile station travels outof one cell and into another cell. Pursuant to the handoff ofcommunication between the access points, the mobile station deassociateswith the serving access point and associates with the target accesspoint.

As noted previously, a brief service interruption sometimes occursduring the handoff of communication between the access points. When thecommunication service forms a voice communication service, theconnection interruption is noticeable, deleteriously affecting the QoS(Quality of Service) of the communication service. Pursuant to operationof an embodiment of the present invention, compensation is made for theservice interruption, and the service quality level of the communicationservice is preserved.

Pursuant to operation of an embodiment of the present invention,apparatus 32 is utilized to selectably to stuff data into data packetcommunicated during a communication session and, specifically, in datapackets that are to be communicated during handoff of communicationsbetween access points. The apparatus includes a data sequence expander34 that operates selectably to stuff data bits into data packets thatare communicated to effectuate a communication service during operationof the communication system. Here, the data bits that form data packetare applied, here represented by way of the line 36, to a buffer 38.Extra data bits are selectably added by the data sequence expander, byway of the line 42, to the data buffered at the buffer 38. The apparatusfurther includes a data sequence contractor 44 that selectably removesdata bits from data packets that are communicated over a radio airinterface upon which data packets are communicated. Here, the datasequence contractor operates upon data buffered at a buffer 46, by wayof the line 48. The buffer buffers data, subsequent to communicationupon the radio air interface, and the data sequence contractor operatesselectably to unstuff data packets that are stuffed with extra databits.

In one implementation, and as shown, the apparatus is embodied at amobile station. In another implementation, also as illustrated, theapparatus is embodied at a proxy device, here a proxy server 50, coupledto the WLAN, or elsewhere at the network portion of the communicationsystem.

Stuffing operations performed by the apparatus are initiated responsiveto preemptive detection of handoff of communications. Here, indicationsare provided, indicated by way of the line 54, of the pendency of thehand-off. Responsive to detection of such indication, the data sequenceexpander becomes operable to stuff data buffered at the buffer 38,forming a de jitter buffer with the additional data bits. And, the data,once stuffed with the additional data bits, is caused to be communicatedupon the radio air interface. And, the data is routed to thecorrespondent entity to be played out thereat.

When the apparatus is embodied at a proxy server, data stuffingoperations are performed thereat. Data communicated on the reverse linkby a mobile station is routed to the proxy server which the apparatus isembodied, and the extra data bits are stuffed. Therein, serviceinterruptions upon the radio air interface during handoff ofcommunications are compensated for, through the addition of the databits at the apparatus embodied at the proxy server. That is to say, thedata bits are added subsequent to service interruption on the radio airinterface. When data is originated at the correspondent entity forcommunication to a mobile station, the data is routed to the proxyserver whereat the extra data bits are added to thereto prior tocommunication upon the radio air interface.

The correspondent entity need not to be aware of the stuffing andunstuffing operations. By embodying the apparatus 32 at the proxy serverat the mobile station, data stuffing and data unstuffing operations areperformed without action required of the correspondent entity. Thecorrespondent entity also need not know of the handoff of thecommunications between access points.

The service quality level of the communications is preserved as delaysare slowly introduced into a real time data stream to make lost packetsbe less noticeable. The delay resulting from the addition of theadditional data bits, forming delay bits, into the data stream is lessnoticeable. The apparatus 32 can also be used in communication systemsthat are also susceptible to communication interruptions, including ininfrastructure-free, i.e., at-hoc wireless communication networks.

FIG. 2-1 through 2-5 illustrate exemplary operations of the apparatus32, here in an implementation in which the apparatus is embodied at themobile station, and data is communicated upon a reverse link from themobile station to the correspondent entity. The buffer 38 is providedwith data, here originated by a sender, i.e., data source, hererepresented at 62. An access point to which data is communicated by wayof reverse link channel defined upon the radio link 16 is also shown.And, a correspondent entity, here a mobile, correspondent entity,referenced also at 26, is positioned to receive data communicatedthereto by the mobile station 12. The correspondent entity includes areceive buffer 64 and a data destination, indicated at RECV 66. Packetflow of packets communicated during normal operation of thecommunication system is also showing in the Figure in which data packets68 are sent at 20 millisecond intervals. The correspondent entity 26here forms an unaware node, and communications of the data packets arecommunicated with minimal buffering as communications here areeffectuated upon a reliable radio link. And, again, the communicationsystem is operated in an infrastructure mode in which communications areeffectuated by way of a network portion of the communication system.

FIG. 2-2 represents operation upon detection of pendency of acommunication handoff from a source access point to a target accesspoint. Data stuffing operations commence. A real-time, quality ofservice (RT QoS) protocol approximates the amount of time required priorto occurrence of handoff of communications, and the real time delay isstarted to be slowly stretched by inserting delay packets, hereindicated at 74, into the real time data packet stream formed of thedata packet 68. If, for instance, a typical 802.11 handoff takes roughly300 ms, and extra 15 data packets are stuffed into the receive buffer 64of the correspondent entity 26 prior to the handoff. The part 66 of thecorrespondent entity place packets from the receive buffer 64 at 20 msintervals. Thus, 15 extra packets create a 300 ms delay in the datapacket stream. Note, in the Figure, that as the mobile station 12 stuffspackets, the receive buffer 64 begins to fill at the correspondententity.

FIG. 2-3 illustrates dissociation, indicated by the X marking 78, withthe source access point. The communication link is temporarily broken.Due to the stuffing of the data packets prior to the handoff ofcommunication, the receive buffer 64 of the correspondent entity is fulland continuous to supply real time data packets even though the link isbroken. Also, here, the mobile station is beginning to buffer its realtime packets 68 so that the packets are sent when the handoff iscomplete and the length returns.

FIG. 2-4 illustrates operation subsequent to association of the mobilestation with a target access point 14-T. Buffered packets 68, bufferedat the send buffer 38 are communicated. When the link returns, thereceive buffer 64 is almost empty. Through proper approximation of thehandoff delay, real time packets delivered by the mobile stations shouldarrive just in time to fill the receive buffer 64 again without breakingthe real time data stream playing at the correspondent entity.

FIG. 2-5 illustrates initiation of unstuffing operations subsequent tohandoff to return the real time delay back to a normal delay period.Unstuffing operations are analogous to stuffing operations. Duringunstuffing operations, the real time data stream is compressed in timedynamically to reduce the delay. Unstuffing is performed over a largeenough period of time to be transparent to the end user of thecorrespondent entity. Any of various stuffing and unstuffing techniquesare utilized to improved the service quality levels of thecommunications.

The real time quality of service protocol on a return path from theunaware node back to the mobile station utilizes a slightly differentapproach by which also to preserve service quality levels. The unaware,correspondent entity 26 does not send out additional data packets inanticipation of a handoff as the unaware entity is oblivious to thestuffing and unstuffing protocol operations. When the correspondententity is a wireline device, the wireline device might also be whollyunaware that communications are effectuated by way of a radio link witha mobile station. The apparatus 36 is embodied, either at a proxy serveror, here, at a mobile station at which to perform the stuffing andunstuffing operations.

FIG. 3-1 illustrates communication of a real time data stream of datapackets, originated at the unaware correspondent entity 26 to the mobilestation 12 when the underlying 802.11 link is good. Real time packets 68are sent at 20 ms intervals. And, both send and receive buffers 64 and38 are empty.

FIG. 3-2 represents operation upon determination that a handoff to atarget access point shall occur soon. And, stuffing operations by whichthe data packets 74 are stuffed into a receive buffer 46 commence. Thecorrespondent entity is unaware of the data stuffing and the stretchingof the real time data packet stream is effectuated by the apparatus 36without knowledge by the correspondent entity of such stuffing. Theamount of real time data stream stretching corresponds to the amount oftime that the pending handoff shall make the link unavailable. Theprocedures are analogous to those shown with respect to FIG. 2-2, exceptthat here, the buffer 46 is being stuffed.

FIG. 3-3 illustrates disassociation, again indicated at 78, of themobile station with a serving access point, prior to association of themobile station with a target access point. The receive buffer 46 of themobile station is full, and the real time data packets are played whilethe link is down. The unaware, correspondent entity never stops sendingreal time packets as the unaware correspondent entity does not realizethe disassociation of the mobile station with the network. All bufferingis performed at the access point, indicated at 86, analogous to thebuffering that occurs when a mobile station indicates to an access pointthat the mobile station is in a power saving mode.

FIG. 3-4 illustrates operation upon association of the mobile stationwith the target access point 14T. The link returns, and the handoffbetween the access point is complete. Buffered packets at the accesspoint are forwarded on to the handset. The buffered data is forwarded tothe target access point by way of an Inter Access Point Protocol (IAPP).The target access point, with which the mobile station is nowassociated, then sends the buffered data packets upon the radio link tothe mobile station. This communication of the data packet fills thereceive buffer 46 of the mobile station.

FIG. 3-5 illustrates unstuffing procedures subsequent to completion ofthe handoff. The unstuffing procedure compresses the real time datastream to return the delay back to normal. As the correspondent entityis unaware of the data stuffing and unstuffing operations, theunstuffing operations are performed without knowledge of thecorrespondent entity.

As noted in FIGS. 3-3 and 3-4, the inclusion of the access point bufferat the access point is needed as the unaware correspondent entity doesnot perform buffering of the data. RT QoS is maintained through theInter Access Point Protocol entities embodied at the access point.Buffered packets are subsequently forwarded to the target access pointssubsequent to handoff by way of the IAPP to avoid being dropped,otherwise negating the benefits of stuffing operations. In a scenario inwhich IAPP does not support handing off buffered packets, a proxy deviceis alternately utilized at the network infrastructure for this purpose.

Stuffing and unstuffing operations stretch and compress, respectively, areal time data packet stream in time. The data packet stream isstretched by adding extra data packets at selected intervals. And,compression of the data packets stream is effectuated by removing theextra data packets.

When a mobile station, such as a mobile station 12, has decided, or hasdetected, that a handoff must occur, data stuffing operations commence.For instance, a determination is made that a handoff shall occur inapproximately two seconds. And, the real time data traffic is flowingfrom the mobile station at 20 ms intervals. Additionally, for instance,the handoff shall make the channel unavailable for 200 ms. A 200 msdelay is injected into the receive buffer of the correspondent entitythrough the stuffing of ten packets into the data stream prior to thehandoff. In two seconds, 2000 ms, the handset shall send out one hundredreal time data packets. Thus, a packet must be stuffed for roughly every10 real time data packets. Conversely, during unstuffing operations, onedata packet is removed out of every ten data packets.

Various methods are available for stretching and compressing real timedata. Most simply, for voice communications, every n.sup.th real timedata packet is replicated when stuffing operations are performed. And,every n.sup.th data packet is dropped during unstuffing operations.Alternately, the audio is stretched-out when stuffing rather than simplyrepeating a data packet. To effectuate this, the mobile stationresamples data to create extra real time data packets and stuffs thereal time data packets into the data stream.

The stretching and compressing of the real time data packets stream is,for instance, effectuated by stuffing and unstuffing during silenceperiods. Voice activity detection senses an audio stream formed of areal time data stream so that the data packets that are stuffed into thereal time data packet stream are stuffed therein during silence periodsonly. In VoIP, the silence periods correspond, e.g., between words, fora conversation, etc.

The previous descriptions are of preferred examples for implementing theinvention, and the scope of the invention should not necessarily belimited by this description. The scope of the present invention isdefined by the following claims.

1. A method comprising: inserting a number of delay packets into asequence of data packets for transmission over a wireless network, thenumber of delay packets being determined based on an estimated amount oftime prior to the occurrence of a hand-off, from a first network accesspoint to a second network access point, such that the insertion of thedelay packets into the sequence of data packets will cause a delay thatcorresponds to the amount of time prior to occurrence of the hand-off.2. The method of claim 1 further comprising: receiving a second sequenceof data packets over the wireless network; and removing delay packetsfrom the received second sequence of data packets in response to theindication of the pending hand-off.
 3. The method of claim 1 wherein theinserting is performed by a mobile communication device.
 4. The methodof claim 1 wherein the inserting is performed by a proxy server.
 5. Themethod of claim 1 wherein the hand-off is a hand-off of a mobilecommunication device from the first network access point to the secondnetwork access point.
 6. The method of claim 1 wherein the wirelessnetwork is a wireless local area network.
 7. The method of claim 1wherein the inserting is inserting the delay packets into the sequenceof data packets while the sequence of data packets are in a buffer.
 8. Amethod comprising: inserting a number of delay packets into a sequenceof data packets for transmission over a wireless network, the number ofdelay packets being determined based on an estimated length of a serviceinterruption, such that the insertion of the delay packets into thesequence of data packets will cause a delay that corresponds to thelength of the service interruption.
 9. The method of claim 8 furthercomprising: receiving a second sequence of data packets over thewireless network; and removing delay packets from the received secondsequence of data packets.
 10. The method of claim 8 wherein theinserting is performed by a mobile communication device.
 11. The methodof claim 8 wherein the inserting is performed by a proxy server.
 12. Themethod of claim 8 wherein the hand-off is a hand-off of a mobilecommunication device from the first network access point to the secondnetwork access point.
 13. The method of claim 8 wherein the wirelessnetwork is a wireless local area network.
 14. The method of claim 8wherein the inserting is inserting the delay packets into the sequenceof data packets that are in a buffer.
 15. The method of claim 8 whereinthe service interruption results from a hand-off of the mobile stationfrom a first network access point to a second network access point. 16.A proxy server comprising: a buffer for buffering a sequence of datapackets; and a data sequence expander for inserting a number of delaypackets into a sequence of data packets, the number of delay packetsbeing determined based on a length of a service interruption such thatthe insertion of the delay packets into the sequence of data packetswill cause a delay that corresponds to the length of the serviceinterruption.
 17. The proxy server of claim 16 wherein the sequence ofdata packets are to be transmitted over a wireless local area network.